Active noise control has been used for many years to reduce the perceived background noise conditions. Acoustical superposition of the background noise and a generated anti-noise signal which is of equal amplitude and opposite phase as the background noise signal results in a null. For example, active noise control has been quite successful in improving the audio experience in headphones that have been sold for use during air travel. Techniques used for these devices have been adapted for use in other electronic devices, including mobile and vehicular radio telephonic devices such as public safety radios and cellular telephones. Active noise control generally requires a reference sensor, an error sensor, computing resources to determine the amount and characteristics of background noise and transducer(s) to output the acoustic anti-noise signal generated. In devices where a separate playback audio signal is present, these resources might be shared. In current active noise control systems, an active noise cancellation (ANC) component and a modified incoming audio (MIA) component are generated. The ANC component and the MIA component are determined independently of each other and are summed together at fixed pre-determined levels that guarantee meeting a system limit that may be determined by one or more of, for example, a digital full scale limit, a rated voltage or rated power of components in the system, pass system requirements such as clipping and distortion metrics, or a user volume setting. In these independent fixed summing systems, the ANC component is determined based on characteristics of the background noise and the MIA component is determined based on the characteristics of the incoming audio source and/or background noise characteristics. The two components are then summed together such that the combined signal will remain within the system limit. In these independent fixed summing systems, the ANC component is sometimes at a low level, and the summed signal does not include the MIA component that is maximized within the system limit. In some embodiments, the MIA component is further constrained by limits imposed on how much gain can be used for the incoming audio.
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